Gas turbine engines for aircraft achieve thrust by discharging hot gases through the exhaust nozzle. Efficient operation for multi-mission application dictates the use of variable area convergent/divergent nozzles.
Variable convergent/divergent configuration is achieved in axisymmetric nozzles by the use of a plurality of circumferentially arranged flaps. Overlapping seals are located between adjacent flaps.
The hinge arrangement must be provided between each convergent flap or seal and each divergent flap or seal. Variations may be made during operation, of the throat and terminal discharge openings.
Increased maneuverability of the aircraft can be accomplished by thrust vectoring. Here the discharge of gas is vectored from the axial direction to achieve a thrust component which is up, down or sideways. As shwon in U.S. Pat. No. 5,082,182 (Bruchez et al, issued Jan. 21, 1992) the vectoring may be accomplished by vectoring movement of the divergent flaps and seals only. The convergent flaps and seals remain symmetrical.
The hinges between the convergent and divergent flap must be capable of rotation around both the radial axis and lateral axis of the hinge. The divergent seal must also maintain a seal against both adjacent flaps at all times to prevent leakage of the hot gas stream and loss of thrust.
During vectoring all of the divergent flaps move in the same direction (i.e. upwardly, to the right, etc.). The divergent flaps thereby become radially offset toward the trailing edges. The seal must be able to maintain contact with these flaps throughout that movement. The seal must be able to twist axially through an angle on the order of 20 degrees from the upstream end to the downstream end in order to maintain this contact, particularly at large nozzle throat areas.
The divergent seal centering device must keep the divergent seal centered between adjacent divergent flaps at large nozzle areas. This must occur whether the nozzle is axial or vectored. Accordingly, the device must tolerate the axial and radial offsets between the divergent flaps when vectored.
The divergent seal restraining device must support the divergent seal at all conditions at which the static pressure on the external side of the seal is greater than that on the internal side. This condition occurs when the nozzle is overexpanded and when the seal is sufficiently vectored away from the gas flow stream.